ArcGIS Pro can't read file geodatabase if extension is uppercase .GDB

Using ArcGIS Pro 2.1.1, I spent an hour banging my head on a file geodatabase that a client sent me. It opens and reads fine in ArcCatalog and ArcMap but couldn't read or open any feature classes in ArcGIS Pro. It turns out the issue was with the folder extension using uppercase letters .GDB. I soon as I changed them to lowercase, all was good.

Steps to reproduce:

Open ArcCatalog create new geodatabase TEST1.gdb

Add a feature class

Close ArcCatalog

Use windows explorer, make a copy of the folder to TEST2.GDB

Open ArcCatalog, both TEST1.gdb and TEST2.GDB are visible and feature class can be seen

Open ArcGIS Pro

Create a new map template project

Try to add feature class from TEST2.GDB

I can't get it display the feature class using the Add Data Button, Adding the database connection or Adding the folder connection.

Close ArcGIS Pro and ArcCatalog

Open windows explorer

Rename TEST2.GDB to TEST2.gdb

Reopen ArcGIS Pro and the test project.

Try to add the feature class from TEST2.gdb, works fine in all three places.